1. Field of the Invention
This invention relates generally to systems and methods for semiconductor fabrication, and more particularly concerns systems and methods for purging a modular isolation chamber such as a standard mechanical interface box or pod used for storing or transporting semiconductor manufacturing materials, to desired levels of relative humidity, oxygen, or particulates.
2. Description of Related Art
A modular isolation chamber such as a standard mechanical interface (SMIF) box, or pod, typically provides a microenvironment to isolate and control the environment surrounding a wafer, cassette of wafers or substrates used in manufacturing integrated circuits, during storage, transport and processing of the materials. Processing of such materials traditionally has been carried out in a particulate free environment generally known as a "clean room". However, maintenance of such "clean rooms" in a contaminant free state can require a great deal of care and effort, particularly during processing of the materials.
In one conventional system in which a SMIF system is used to replace a traditional clean room, filtered air is circulated in the SMIF box, and still air is used to achieve cleanliness in the SMIF box. A particle-free dockable interface for linking together two spaces each enclosing a clean air environment includes interlocking doors on each space that fit together to trap particles which have accumulated from the dirty ambient environment on the outer surfaces of the doors. A processing apparatus and technique is also known for thermal processing in the manufacture of semiconductor devices, to prevent outside air from entering a reaction tube. Loading and unloading an object to be processed is typically effected by an insertion jig outside a heating section, to prevent outside air from entering the heated processing chamber.
While such systems can control the level of particulates in a SMIF box, the presence of oxygen can also degrade the surface of semiconductor materials. In one conventional process for preventing the formation of native oxides on the surface of semiconductor materials, silicon nitride layers are formed on silicon substrates. Purge systems are also known, such as one in which a movable cantilevered purge system provides for a wafer load position, a wafer purge position, and a wafer process position. A purge injector and return exhaust tube are provided in an elephant tube which provides for access to wafer loads. In another known system, the manufacturing materials are subjected to cold nitrogen purge cycles, and particles and particle-generated defects during gas phase processing such as during deposition are decreased by controlling particle transport mechanisms, such as by applying low level radiant energy during cold nitrogen purge cycles.
The presence of humidity in a SMIF box can also be undesirable. One conventional method and apparatus for cleaning integrated circuit wafers utilizes dry gases. At least one of the gases is excited by passing the gas through a microwave plasma generator or by heating the wafer, exciting the gases near the surface of the wafer, causing chemical reactions similar to those induced by ionization of nongaseous cleaning materials in water. After an etching period, the etching chamber is purged by inert gas, such as nitrogen, which helps carry away the remaining reacted contaminants, which can include vaporous halogens or radicals that can be present after conventional processes, such as chlorine, bromine, arsine, silane, and the like.
However, there remains a need for a system and method of purging SMIF pods to consistently maintain desired levels of relative humidity, oxygen, or particulates while the pods are otherwise not required, such as while waiting for a next production station or step in a fabrication facility. These periods have been estimated to be about six minutes to several hours long. Ideally, the SMIF pod should be completely purged to desired levels of relative humidity, oxygen, or particulates in a period of about 6 minutes or less. The present invention meets these needs.